Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session S22: Charged and Ion-Containing Polymers |
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Sponsoring Units: DPOLY Chair: Yossef Elabd, Drexel University Room: 407 |
Thursday, March 6, 2014 8:00AM - 8:12AM |
S22.00001: Chain Dynamics and Layering within Spin-Assisted versus Dip-Assisted Polyelectrolyte Multilayer Assemblies Aliaksandr Zhuk, Victor Selin, John F. Ankner, Svetlana Sukhishvili We report on the effect of deposition technique on polyelectrolyte (PE) chain dynamics within layer-by-layer (LbL) films, and on the stability of these films in salt solutions. Spin-assisted LbL (SA-LbL) films demonstrated a higher degree of film stratification, as well as greater salt stability, compared to dip-coated assemblies. Lateral and vertical polyelectrolyte diffusion of PE chains within LbL films, measured by fluorescence recovery after photobleaching (FRAP) and neutron reflectometry (NR), respectively, revealed a much higher degree of anisotropy for SA-LbL films as compared to dip-coated multilayers, with diffusion coefficients $\sim$ 10$^{6}$ larger in parallel to the substrate versus those in the perpendicular direction. The data suggest that the degree of PE chain flattening and film stratification significantly affects PE chain dynamics and film behavior in salt solutions. [Preview Abstract] |
Thursday, March 6, 2014 8:12AM - 8:24AM |
S22.00002: Temperature-triggered transformations in shape of layer-by-layer microtubes in aqueous media Choonghyun Sung, Ajay Vidyasagar, Katelin Hearn, Jodie Lutkenhaus Nano- and microstructured layer-by-layer (LbL) assemblies have been of considerable interest for various applications. In particular, one-dimensional LbL microtubes have garnered interest for their ability to shrink or swell in response to changes in pH. Temperature has also been known to trigger transformations in shape. In this presentation, we report on the thermal behavior of LbL microtubes of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA). PAH/PAA LbL microtubes were prepared using polycarbonate membranes as porous templates. The thermal behavior of both freely released microtubes and template-bound microtubes was investigated in aqueous media as a function of temperature and time using confocal laser scanning microscopy and scanning electron microscopy. When free microtube suspensions were incubated at high temperatures, the microtubes became shorter and ellipsoid in shape. In contrast, the template-bound microtubes showed periodic voids on the surface. In both cases, pronounced transformations occurred above the hydrated glass transition temperature of the PAH/PAA LbL microtube. [Preview Abstract] |
Thursday, March 6, 2014 8:24AM - 8:36AM |
S22.00003: Dynamics of Precise Ethylene-Acrylic Acid Copolymers and Ionomers Using Dielectric Spectroscopy James Runt, U Hyeok Choi, Hanqing Masser, C. Francisco Buitrago, L. Robert Middleton, Karen Winey, Joseph Cordaro, Amalie Frischknecht This investigation focuses on a molecular-level understanding of the dynamics of novel copolymers, consisting of monodisperse ethylene sequences between very precisely spaced acrylic acid or ionic functionality. Incorporating ions in precise acid copolymers(via neutralization of a portion of the acid functionality) results in significant changes in the association state of the acid and ionic groups, as well as polymer and ion dynamics. The dynamics of these materials were explored over a wide temperature and frequency range using dielectric spectroscopy. Acid copolymers exhibit two local relaxations in the glassy state and a segmental relaxation above T$_{\mathrm{g}}$. In addition, two slower relaxations above T$_{\mathrm{g}}$ were observed in ionomers, and their origin will be discussed in the presentation. For example, the highest temperature process is assigned to Maxwell-Wagner-Sillars (MWS) interfacial polarization, associated with the microphase separated structure. A transition in the MWS relaxation frequency and strength is observed around the melting point of copolymers with sufficiently long ethylene sequences, suggesting that the MWS process in these materials is strongly correlated with crystallinity of the ethylene backbone. [Preview Abstract] |
Thursday, March 6, 2014 8:36AM - 8:48AM |
S22.00004: Plastic Deformation and Morphological Evolution of Precise Acid Copolymers L. Robert Middleton, Jason Azoulay, Dustin Murtagh, Joseph Cordaro, Karen Winey Acid- and ion-containing polymers have specific interactions that produce complex and hierarchical morphologies that provide remarkable mechanical properties. Historically, correlating the hierarchical structure and the mechanical properties of these polymers has been challenging due to the random arrangements of the polar groups along the backbone, ex situ characterization and the difficulty in deconvolution the effects of crystalline and amorphous regions along with secondary interactions between polymer chains. We address these challenges through in situ deformation of precise acid copolymers and relate the structural evolution to bulk properties by considering a series of copolymers with 9, 15 or 21 carbons between acid groups. Simultaneous synchrotron X-ray scattering and room temperature uniaxial tensile experiments of these precise acid copolymers were conducted. The different deformation mechanisms are compared and the microstructural evolution during deformation is discussed. For example, the liquid-like distribution of acid aggregates within the bulk copolymer transitions into a layered structure concurrent to a dramatic increase in tensile strength. Overall, we evaluate the effect and control of introducing acid groups on mechanical deformation of the bulk copolymers. [Preview Abstract] |
Thursday, March 6, 2014 8:48AM - 9:00AM |
S22.00005: Morphology and Water Uptake in Block Copolymer Electrolyte Membranes Xi Chen, David Wong, Sergey Yakovlev, Keith Beers, Nitash Balsara Polymer electrolyte membranes (PEMs) consisting of proton-conducting hydrophilic channels and a mechanically-strong hydrophobic matrix are attractive due to their wide clean energy applications. In an effort to understand the fundamentals of proton transport in PEMs, we fabricated a series of non-porous and mesoporous sulfonated poly(styrene-b-ethylene-b-styrene) (S-SES) copolymer membranes. We examine the effects of porosity and humidity level on the morphology of S-SES membranes. The relationship between morphology and water uptake of the membranes at different humidity levels are established. We show that by controlling the porosity of the membranes, we are able to optimize the water uptake of the membranes at desired humidity levels to maximize proton conductivity. Furthermore, we show the in situ morphology change of the membranes from fully hydrated state to dry state in a drying experiment. Morphology and water content of the membranes as a function of time are examined. [Preview Abstract] |
Thursday, March 6, 2014 9:00AM - 9:12AM |
S22.00006: Morphology and Ionic Conductivity of Humidity-Responsive Polymerized Ionic Liquid Block Copolymers Sharon Sharick, Kelly Meek, Yuesheng Ye, Yossef A. Elabd, Karen I. Winey We present the ionic conductivity and morphology of humidity-responsive polymerized ionic liquid block copolymers (PIL BCPs), poly(methyl methacrylate-$b$-1-[2-(methacryloyloxy)ethyl]-3-butylimidazolium-X), where X is a bromide (Br) or hydroxide (OH) anion, as a function of relative humidity (RH), temperature, and PIL composition ($\phi_{PIL})$. PIL BCPs were characterized by in situ small-angle X-ray scattering and electrochemical impedance spectroscopy. These PIL BCPs have microphase separated morphologies and long-range order increases as $\phi_{PIL}$ increases. Notably, ionic conductivity increases 3 to 4 orders of magnitude when RH increases from 30 to 90 percent. When $\phi_{PIL}$ is greater than 0.37, BCP ionic conductivity approaches or exceeds that of the homopolymer, suggesting that the dynamics in PIL microdomains mimic the homopolymer and long-range order aids ion transport. Moreover, over 60 percent of the BCP is nonconductive without a penalty in ion transport. When $\phi_{PIL}$ is less than 0.37, BCP conductivity is 1 to 2 orders of magnitude less than the homopolymer and non-conductive PMMA segments dominate ion transport, as expected. Ionic conductivities at 80 $^{^{\circ}}$C, 90 percent RH, are 7.6 mS/cm for the Br-containing BCP with $\phi_{PIL} \quad =$ 0.53 and 25.0 mS/cm for the OH-containing BCP with $\phi_{PIL} \quad =$ 0.50. [Preview Abstract] |
Thursday, March 6, 2014 9:12AM - 9:24AM |
S22.00007: Conformation of cellulose based polyelectrolyte NaCMC in solution: Effect of concentration and solvent quality Carlos Lopez, Joao Cabral, Peter Graham, Ralph Colby We report small angle neutron scattering (SANS) experiments on the crossover between semidilute entangled and concentrated regimes as well as the effect of a non-solvent in the conformation of sodium carboxy methyl cellulose (NaCMC), a semi-flexible polyelectrolyte. We investigate solvation and extract the correlation length dependence on concentration, solvent quality and salt content, up to eventual peak disappearance. While a sharp change is observed in rheological measurements at the crossover to the concentrated regime, only a small change or no change in the scaling of the correlation length is measured by SANS, depending on solvophobicity. The addition of a non solvent causes an increase in the low wavenumber (q) range but has little or no effect on the magnitude of the correlation length, in contrast to conductivity measurements which show a significant amount of counterion condensation. [Preview Abstract] |
Thursday, March 6, 2014 9:24AM - 9:36AM |
S22.00008: A new insight into the counterion distribution of charged polymer brushes Xiao Chu, Guangming Liu, Jiang Zhao Counterions distribution of a number of polyeletrolyte brushes are investigated using a combination of methods as QCM-D, ellipsomety and single molecule fluorescence microscopy. The experiemtnal evidence show that, as the salt level increases, counterions penetrate into the brushes, bringing about enhanced swelling and mechanical response of the brushes. The results have privided a new picture about counterion distribution of charged polymer brushes. [Preview Abstract] |
Thursday, March 6, 2014 9:36AM - 9:48AM |
S22.00009: Macroion induced dehydration of weak polyelectrolyte brushes Zhongli Zheng, Y. Elaine Zhu The interaction of macroions, including polyelectrolytes, DNAs, and proteins, with polymer and cellular surfaces is critically related to many biomolecular activities, such as protein adsorption and DNA hybridization at probe surfaces. In an experimental approach to examine the macroion electrostatic interaction with a polymer surface while minimizing the long-debated hydrophobic interaction, we study the interaction of molybdenum-based inorganic polyoxometalate (POM) nanoclusters carrying 42 negative charges as model hydrophilic macroions with surface-tethered poly-2-vinylpyridine (P2VP) brushes immersed in aqueous solutions. By AFM, QCM, and contact goniometer, we have observed the collapse of P2VP chains by adding POM macroions at a constant pH. Surprisingly, added POM macroions can cause the shift of swollen-to-collapse transition pH to a lower value, in contrast to the shift to high pH value by adding simple monovalent salts. At sufficiently high POM concentration, a stable POM-P2VP composite layer, showing little dependence on solution pH and additional salts, can be formed, suggesting a simple route to construct meso-porous polymer membranes. [Preview Abstract] |
Thursday, March 6, 2014 9:48AM - 10:00AM |
S22.00010: Self-assembly of polyelectrolyte surfactant complexes using large scale MD simulation Monojoy Goswami, Bobby Sumpter Polyelectrolytes (PE) and surfactants are known to form interesting structures with varied properties in aqueous solutions. The morphological details of the PE-surfactant complexes depend on a combination of polymer backbone, electrostatic interactions and hydrophobic interactions. We study the self-assembly of cationic PE and anionic surfactants complexes in dilute condition. The importance of such complexes of PE with oppositely charged surfactants can be found in biological systems, such as immobilization of enzymes in polyelectrolyte complexes or nonspecific association of DNA with protein. Many useful properties of PE surfactant complexes come from the highly ordered structures of surfactant self-assembly inside the PE aggregate which has applications in industry. We do large scale molecular dynamics simulation using LAMMPS to understand the structure and dynamics of PE-surfactant systems. Our investigation shows highly ordered pearl-necklace structures that have been observed experimentally in biological systems. We investigate many different properties of PE-surfactant complexation for different parameter ranges that are useful for pharmaceutical, engineering and biological applications. [Preview Abstract] |
Thursday, March 6, 2014 10:00AM - 10:12AM |
S22.00011: Surface tension of polyelectrolyte coacervates Jian Qin, Dimitrios Priftis, Robert Farina, Sarah Perry, Lorraine Leon, Jonathan Whitmer, Kyle Hoffman, Matthew Tirrell, Juan J. de Pablo Stoichiometric solutions of polycations and polyanions can phase separate, resulting in the coexistence of a supernatant phase and a polymer-rich complex phase. The complex phase may be liquid-like or solid-like, depending on the ionic strength and the temperature. Liquid-like complexes, known as ``coacervates'', retain a large amount of water, up to 70-80\% by weight, and exhibit an ultra-low interfacial tension with the coexisting supernatant phase (smaller than the water surface tension by three orders of magnitude). Previous experiments have observed that this interfacial tension decreases with the amount of salt, and vanishes near a critical salt concentration according to a $3/2$ power of the salt undersaturation. In this work we derive analytical expressions for the interfacial tension in both the low and high charge density limits. For solutions with added salts, we provide explicit expressions for the interfacial tension near the critical salt concentration and explain the $3/2$ power dependence. Our results are shown to be in good agreement with experiment. [Preview Abstract] |
Thursday, March 6, 2014 10:12AM - 10:24AM |
S22.00012: Multiscale simulation of complex coacervates Kyle Q. Hoffmann, Jonathan K. Whitmer, Jian Qin, Dimitris Priftis, Sarah Perry, Lorraine Leon, Matthew Kade, Matthew Tirrell, Juan J. de Pablo Aqueous solutions of polymers having opposite charge can separate into a coacervate phase and a supernatant water phase.The conditions leading to such behavior, including chain lenght, ionization fraction, ionic strength, molecular structure, and temperature are poorly understood. Though thermodynamic models of this phase separation exist, they offer little descriptive power for the mechanism of complex coacervation, and the internal structure of the coacervate and precipitate phases. Here we use atomic-level and coarse-grained representations of polypeptides to study features of the phase diagram, scaling relations, and microstructure of complex coacervates, comparing results to experimental data and model calculations. [Preview Abstract] |
Thursday, March 6, 2014 10:24AM - 10:36AM |
S22.00013: Polyelectrolyte (PE) induced interactions between Charged and zwitterionic Colloids Victor Pryamitsyn, Venkat Ganesan A numerical self-consistent field (SCF) theory approach was developed for studying mixture of polyelectrolytes with charged and uncharged nanoparticles. Such an approach was used to analyze within the mean-field limit the polyelectrolyte-mediated effective interactions between the particles. The system considered allows for the local PE and particle charges to be defined by the local concentration of ionizable on groups on the particles and polyelectrolytes, ambient conditions like pH and the local electrostatic potential. Calculation of the free energy of a system of one, two and three particles in the polyelectrolyte solution allowdd us to calculate the particle insertion free energy, two and three body particle-particle interactions as a function of the properties of solution, polymer-particle interactions and the particle size. For the situation involving acidic PE and a base type positively charged particles, the PE mediated particle-particle interaction is purely repulsive for the larger particle-particle distances at low polymer concentrations. At short-particle particle distances and/or higher polyelectrolyte concentrations the particle-particle interaction becomes a depletion-type attraction. For Zwitterionic positively chaged paticles particles we have found a a range [Preview Abstract] |
Thursday, March 6, 2014 10:36AM - 10:48AM |
S22.00014: Dispersing Functionalized Nanoparticles in PEO-based Single Ion Conductors Michael O'Reilly, Karen Winey Lithium single-ion conductors have the potential to reach high lithium transference numbers and high viscosities, but demonstrate poor ion transport properties. Ion mobility is inversely related to structural rigidity, so the highest ionic conductivity is usually achieved by ionomers with the most liquid-like properties. Solid nanofillers designed to enhance ion dynamics at the particle-polymer interface may improve the viscosity of an ionomer without arresting ion mobility. We demonstrate how silica nanoparticles are functionalized for favorable and unfavorable interactions with a sulfonated PEO-based ionomer matrix. We find that nanoparticle surface chemistry and loading fraction have implications on thermal properties, nanoparticle dispersion, viscosity, and lithium conduction. For functional groups designed for favorable ionomer interactions but poor nanoparticle dispersion, the viscosity of the nanocomposite may be altered significantly while negligibly affecting ionic conductivity even at high volume fractions of non-ionic filler. [Preview Abstract] |
Thursday, March 6, 2014 10:48AM - 11:00AM |
S22.00015: Dramatic Changes in Polyelectrolyte Blend Phase Behavior due to Charge Correlations Monica Olvera de la Cruz, Jos Zwanikken, Charles Sing Polymer blends are typically used to impart a unique combination of properties to a material using a blend of two or more common homopolymers. Designing such systems requires knowledge of the mixing thermodynamics of the two polymers being blended; if one species is charged (e.g. an ionomer), then the thermodynamics is highly dependent on both the tendency of the system to mix (via the ubiquitous Flory $\chi$-parameter) and the electrostatics of the charged polymer backbone and the corresponding counterions. While mean-field theories treat the former well, the latter is difficult in low dielectric constants due to the inadequacy of perturbation theories in describing highly-correlated charged structures. We demonstrate that a new hybrid liquid state integral equation-self consistent field theory (LS-SCFT) calculation can provide articulation of both local charge correlations as well as macroscopic thermodynamics, and show that these correlations can profoundly affect polyelectrolyte blend phase behavior. Ultimately, even polymers that mix at all temperatures ($\chi N= 0$) can be driven to phase separate upon inclusion of charges. [Preview Abstract] |
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